The present invention relates to an exhaust system for an internal combustion engine including a flow-regulating valve responsive to pressure in the system.
Performance and efficiency of internal combustion engines are affected by the characteristics of their exhaust systems. When designing an exhaust system, compromises must be made concerning engine performance at different speeds. For a static exhaust system, pressure downstream of the engine will vary with engine speed. Low or negative pressure helps to suck exhaust gas from the combustion chamber and, during valve overlap, to draw in a fresh fuel-air mixture. On the other hand, high positive pressure interferes with expulsion of exhaust gas from the engine and, during valve overlap, interferes with the incoming air-fuel mixture. Thus it is important to get the an appropriate amount of pressure at the downstream locations.
Particularly for high performance engines in which exhaust systems are designed to minimize pressure during valve overlap at high engine speeds for maximum power, exhaust systems have been proposed with special mufflers having throttle valves to restrict exhaust flow through the mufflers at low engine speeds in order to lessen or eliminate xe2x80x9cback pressure.xe2x80x9d
One such systems is described in U.S. Pat. No. 5,355,673. This patent describes an exhaust valve that can be incorporated in an otherwise conventional exhaust system, preferably by coupling to the exhaust end of the conventional exhaust pipe. The ""673 valve has an internal butterfly valve which is spring-biased to an essentially closed position to restrict flow through the pipe. However, under high flow conditions the valve is swung against the force of the biasing spring to an open position in which flow is essentially unrestricted. Under back pressure conditions, the valve swings oppositely, but still constitutes a substantial obstruction to exhaust flow.
A linkage assembly provides biasing components that respond to the pressure conditions within the tube and seek to return the valve to a neutral stance. The assembly includes a pair of elongated links positioned adjacent one another. A single compression spring is held along the overlap portion. During high flow or back pressure conditions, the plate moves the links apart from one another, causing compression of the single spring. Once the pressure is relieved, the compressed spring moves the plate back to its neutral position.
While this system is acceptable, repeated compression of the spring may lead to a loss of spring compression. This can cause the linkage assembly to become sluggish in returning the valve plate to its neutral position. Thus, a need exists for a linkage assembly that avoids causing spring compression loss. The present invention is directed to this need and others as described below.
In accordance with the present invention, a linkage assembly is described for use with an exhaust valve having an exhaust tube. The linkage assembly includes a crank arm, first and second elongated links, and first and second springs. One end of the first link is rotatably connected to the crank arm. One end of the second link is rotatably connected to the tube. The remaining ends of the links are adjacent one another and overlap. The first spring is held within this overlapping portion. The second spring is held about the second link.
The linkage assembly includes a neutral position in which the first and second links are generally transverse with the crank arm and the first and second springs are balanced in force. An open position is provided in which the crank arm is rotated to move the first and second links away from one another, causing the second link to be less compressed than the first link. A back pressure position is also provided in which the crank arm is rotated to move the first and second links toward one another, causing the first link to be less compressed than the second link.
In accordance with other aspects of the invention, in one embodiment, both the first and second springs are held in compression in the neutral, open, and back pressure configurations.